The regulation of ketone body and free fatty acid (FFA) metabolism will be studied in intact fasting rats. Blood FFA concentrations will be increased by either infusing chylomicrons and heparin or by infusing an oleic acid emulsion. Effects of these infusions on blood concentrations of FFA and ketone bodies and on their turnover rates will be compared. These experiments will also be done using rats made diabetic with streptozotocin.